What must you do after attaching a semitrailer?

After attaching a semitrailer, it is essential to ensure safety and proper functioning before driving. First, you must check the fastening and locking system of the fifth wheel to confirm that the semitrailer is securely connected to the tractor unit. This prevents the trailer from accidentally detaching while driving. Second, you need to connect and check all hoses and cables, including air brake lines and electrical connections, to ensure brakes and lights work correctly. The third option, releasing the reverse lock, is not mandatory after every attachment; it is a specific step that may be necessary only in certain situations. Therefore, focusing on securing the connection and verifying all connections are intact is the required procedure according to German traffic regulations.